1. Field of the Invention
The present invention relates to an apparatus for simultaneously determining the thickness and composition of a multi-layered sample in a nondestructive manner and, more particularly, to an X-ray coating thickness gauge for measuring an alloy plating layer thickness and copper concentration without being influenced by the material itself when the sample to be measured is a tin-copper alloy plating layer provided on a copper alloy material.
2. Description of the Related Art
Fluorescent X-ray thickness measuring devices by which fluorescent X-rays are acquired from a multilayer sample using an X-ray generator and an energy dispersive type X-ray detector, with a layer thickness and an alloy composition then being measured using a calibration curve method or a theoretical calculation method, are well known and are widely used in determining the thickness and composition of solder, for example.
In recent years, the development of lead-free solder has been progressing due to demands for environmentally friendly products. One of these has been the development and use of tin-copper alloy plating or tin-silver-copper alloy plating, with the thickness and management composition of these platings being requested by quality
A method for measuring alloy plating thickness and composition using X-ray fluorescence techniques is disclosed, for example, in Japanese Patent Laid-open No. Sho. 61-84511. This method is described simply in the following as an example applied to measuring a sample of tin-copper alloy plating.
When X-rays from an X-ray generator irradiate the sample, tin fluorescent X-rays (hereinafter referred to as Sn—K X-rays) and copper fluorescent X-rays (hereinafter referred to as Cu—K X-rays) are emitted from the tin and the copper within the alloy plating.
At this time, an intensity NS of the Sn—K X-rays and an intensity NC of the Cu—K X-rays increase as the thickness of the alloy plating increases. Further, the intensity NC of the Cu—K X-ray increases as the concentration w of copper increases. This is expressed in the form of an equation in the following manner.NS=f(t, w)NC=g(t, w)
A series of standard materials is measured in advance, parameters for these coefficients are determined, the measured intensity obtained from the as-yet unknown material is substituted so that a simultaneous equation is solved to determine the thickness of the plating and the concentration of the copper.
However, problems are encountered when measuring a sample where a tin-cooper alloy plating is applied on a copper material. Namely, when this kind of sample is irradiated with X-rays, Cu—K X-rays are emitted from the copper within the alloy plating and the copper of the material. When the thickness of the alloy plating increases, the intensity of the Cu—K X-rays emitted from the copper within the alloy plating increases but the intensity of the Cu—K X-rays emitted from the copper of the material conversely reduces due to being absorbed by the plating layer. Therefore, measurement is not possible because even if a consecutive standard agent group can be measured, parameters for the relational expression may be indeterminate, and even if a parameters can be determined, the simultaneous equation cannot be solved or the calculation results are unstable.